1. Field of the Invention
This invention relates to a method and apparatus for earth boring in which the apparatus is locatable at least partially within a borehole. More particularly, this invention relates to a method and apparatus that utilizes high power lasers for earth boring in which an array of optical fibers is constructed and arranged to be positioned downhole in an earth boring operation in communication with a focal lens array, thereby directing laser energy at the earth to break and melt rock.
2. Description of Related Art
The use of lasers for the purpose of producing boreholes to enable the extraction of liquid and gaseous fuels from underground formations is well-known in the art. For example, U.S. Pat. No. 4,266,609 to Rom et al. teaches a method of extracting liquid and gaseous fuels from oil shale and tar sand. Using this method, kerogen and other materials can be extracted by drilling boreholes in a selected pattern through the overlying soil and rock without removing it. Each borehole mouth is closed by a cover provided with an air inlet pipe and a gas exhaust pipe. A laser beam generated by a laser source is introduced into the upper end of the pipe and directed centrally to its bottom where it is diverted toward the borehole wall by a mirror assembly. The laser beam moves along the borehole wall and irradiates the oil shale or tar sand, igniting the combustible matter contained therein, which liquefies and evaporates. This method does not utilize the laser energy to further create the hole, but rather it ignites and burns what otherwise may be valuable recoverable fossil fuels in an effort to extract, through the gas generation, liquid and gas by more conventional means.
U.S. Pat. No. 4,066,138 to Salisbury et al. teaches an earth boring apparatus mounted above ground that directs an annulus of high powered laser energy downwardly for boring a cylindrical hole by fusing successive annular regions of the stratum to be penetrated at a power level that shatters and self-ejects successive cores from the hole. A first fluid blast above the hole deflects the ejected core as it exits from the hole and a second fluid blast above the hole ejects fluid to provide adequate fluid at the strata to be penetrated prior to actuation of the laser for promoting a thermal shock capable of shattering and ejecting the core. Optical sensing separately detects the core shattering and the core ejection to control timed actuation of the system components. Clearly one limitation of this system is its inability to drill non-linear boreholes. In addition, generation of the desired annular pattern as well as controlling timed actuation of the system components requires a reasonably complex arrangement of equipment.
U.S. Pat. No. 4,282,940 to Salisbury et al. teaches an apparatus for perforating oil and gas wells. Using this method, a high-powered coherent light beam is axially directed along the borehole to a predetermined depth and deflected along a beam axis. The beam is focused to concentrate at each of a plurality of spaced focal points along the deflected beam. This, in turn, is said to provide a significant increase in the distance that calculated oil or gas bearing formations can be perforated, thereby increasing the yield by more conventional means.
The use of lasers for drilling is also taught by U.S. Pat. No. 4,113,036 to Stout in which underground boreholes are drilled through a formation from a plurality of vertical boreholes by use of laser beams to form a subsurface, three-dimensional bore passage pattern for in situ preparation of fossil fuel deposits to be recovered and a laser beam is projected vertically through an angularly adjusted tubular housing inserted into each borehole from which a reflected drilling beam is laterally directed by an angularly adjusted reflector to form a bore passage; U.S. Pat. No. 3,871,485 to Keenan, Jr. in which a laser beam generator positioned in a wellhole is electrically connected to an inhole voltage generator actuated by drilling mud or other liquid passing through a laser beam housing connected to the drill string and a reflecting crystal for the laser beam is positioned within the laser beam housing to reflect the beam in an elliptical pattern across the formation to be penetrated; U.S. Pat. No. 4,090,572 to Welch in which a laser beam for drilling gas, oil or geothermal wells in geological formations and for xe2x80x9cfracingxe2x80x9d the pay zones of such wells to increase recovery is projected into a wellbore along a beam guide so as to make available laser energy adequate to melt or vaporize the formation under downhole conditions; and U.S. Pat. No. 5,107,936 to Foppe in which a gap defining the outer profile of a borehole is melted down and the drill core surrounded by this gap is extracted at intervals through the melting zone.
It will be apparent to those skilled in the art that several of these apparatuses require the use of complex and fragile equipment and some of these apparatuses are inherently expensive, difficult to operate properly, difficult to maintain and exceedingly fragile, particularly in view of the hostile environment in which they are used. Thus, there is a need for high powered laser drilling equipment that addresses each of these issues.
Another problem associated with conventional methods and apparatuses that utilize high power lasers for fossil fuel recovery is that they require the use of movable mirrors, which are difficult to position and to control.
Yet a further problem associated with conventional methods and apparatuses employing high power lasers for fossil fuel recovery is that they utilize many moving parts that cannot be readily maintained in the field.
Still a further problem associated with conventional methods and apparatuses employing high power lasers for fossil fuel recovery is that they require a complex assortment of relatively minute components that are susceptible to damage from numerous adverse conditions in the field, particularly in view of the surrounding hostile environment.
Yet another problem associated with conventional methods and apparatuses employing high power lasers for fossil fuel recovery is that they are not adaptable to directional drilling or holes that are other than straight.
An even further problem associated with conventional methods and apparatuses employing high power lasers for fossil fuel recovery is that a laser beam directed downward into a hole is subject to dissipation and misdirection due to the presence of fluid, dust and/or other materials within the hole.
Accordingly, it is one object of the present invention to provide a method and apparatus for earth boring using high powered lasers that seeks to overcome the problems discussed above and which is readily adaptable to a variety of applications.
More particularly, it is one object of this invention to provide a downhole lens assembly for use in connection with high-powered lasers for earth boring that does not require complex apparatuses which are difficult to maintain in the field.
It is another object of this invention to provide a downhole lens assembly for use in connection with high-powered lasers for earth boring that does not require the use of movable mirrors which are difficult to position and control.
It is yet another object of this invention to provide a downhole lens assembly for use in connection with high-powered lasers for earth boring that does not require many moving parts that cannot be readily maintained in the field.
It is still a further object of this invention to provide a downhole laser assembly for use in connection with high-powered lasers for earth boring that does not require a complex assortment of minute components that are susceptible to heat damage and damage from other adverse conditions in the field.
Additionally, it is an object of this invention to provide a downhole lens assembly for use in connection with high-powered lasers for earth boring that is adaptable to use when the path of a bore is not straight, thereby rendering the apparatus suitable for directional drilling.
Still a further object of this invention is to provide a downhole lens assembly for use in connection with high-powered lasers for earth boring that transfers the laser energy downward into the hole so that it is not subject to dissipation and misdirection due to the presence of fluid, dust and/or other materials within the hole.
These and other objects of this invention are addressed by an earth boring apparatus that is at least partially locatable within a borehole, which apparatus comprises a plurality of optical fibers, each of which has a proximal fiber light energy input end and a distal fiber light energy output end. At least one focal lens is disposed at the distal fiber light energy output end of the plurality of optical fibers, which focal lens comprises a plurality of focal elements, each of which corresponds to the distal fiber light energy output end of at least one of the optical fibers and which is arranged to receive light energy from the corresponding distal fiber light energy output end of the at least one optical fiber and focus the light energy outward from the distal fiber light energy output end. In accordance with a particularly preferred embodiment, the plurality of optical fibers are disposed in a flexible casing, thereby forming an optical fiber bundle. Because the progress of the apparatus in the borehole does not depend on crushing the rock by application of weight as in conventional drilling systems, the entire apparatus may be constructed of much lighter weight materials, such as fiber reinforced composites.